1. Field of Invention
The present invention relates to a motor control technique; and more particularly relates to a motor control technique that can be used to control the flow of fluids from a pump.
2. Description of Related Art
There are many devices used to measure the rotation of a motor shaft.
A dynamometer measures the rotation of a motor shaft by mechanically coupling the shaft to a rotation sensor.
An encoder is another device which is mechanically coupled to the motor shaft. An encoder uses a patterned wheel which can contain holes for an optical sensor, magnets for a magnetic sensor, or contacts for an electric sensor. Another method to measure the rotation of a motor relies on the back EMF generated by the rotating core during the off time of a PWM voltage which is used to drive the motor, this method is described in US 20130081718 A1.
One problem with the known techniques used in the above mentioned devices, is that any device which is mechanically coupled to a motor, as is the case with the dynamometer and encoder, will require work from the motor to provide its motion. This work will increase the load on the motor. Another shortcoming is that these methods require external devices mechanically coupled to the motor shaft in order to operate. These external devices add extra cost and complexity to any system in which they are installed. There are also many situations in which the space requirements of the system preclude the use of any external devices mounted on the motor shaft.
The method described by US 20130081718 A1 using the back EMF of the rotating core to determine a motor's rotational speed has several shortcoming. It is sensitive to unwanted electrical noise, is dependent on measurements taken when the applied voltage is drastically changed, and also requires temperature correction due to the temperature dependency of the physical properties the system uses to infer motor rotation.